Aluminum alloy sheet for lithographic printing plate and method of producing the same

ABSTRACT

An aluminum alloy sheet for a lithographic printing plate which allows pits to be more uniformly formed by an electrochemical surface-roughening treatment and exhibits more excellent adhesion to a photosensitive film and water retention properties, and a method of producing the same are disclosed. The aluminum alloy sheet includes 0.1 to 1.5% of Mg, more than 0.05% and 0.5% or less of Zn, 0.1 to 0.6% of Fe, 0.03 to 0.15% of Si, 0.0001 to 0.10% of Cu, and 0.0001 to 0.05% of Ti, with the balance being aluminum and impurities, the Mg content and the Zn content satisfying a relationship “4×Zn %−1.4%≦Mg %≦4×Zn %+0.6%”, and the amount of aluminum powder on the surface of the aluminum alloy sheet being 0.1 to 3.0 mg/m 2 . It is more effective when precipitates with a diameter (circle equivalent diameter) of 0.1 to 1.0 μm are dispersed on the surface of the sheet in a number of 10,000 to 100,000 per square millimeter (mm 2 ).

TECHNICAL FIELD

The present invention relates to an aluminum alloy sheet for a lithographic printing plate. More particularly, the present invention relates to an aluminum alloy sheet for a lithographic printing plate which can be surface-roughened uniformly by an electrochemical etching treatment and exhibits excellent strength and thermal softening resistance, and a method of producing the same.

BACKGROUND ART

An aluminum alloy sheet is generally used as a support for a lithographic printing plate (including an offset printing plate). Such a support is surface-roughened from the viewpoint of improving adhesion to a photosensitive film and improving the water retention properties in a non-image area. As the surface roughening method, a mechanical surface roughening method such as ball graining, brush graining, or wire graining has been employed. In recent years, a method of roughening the surface of a support aluminum alloy sheet by an electrochemical etching treatment has been increasingly developed due to excellent plate-making applicability (fitness), excellent printing performance, and a continuous treatment capability using a coil material.

The electrochemical etching treatment is performed using hydrochloric acid or an electrolyte mainly containing hydrochloric acid (hereinafter referred to as “hydrochloric acid-based electrolyte”), or nitric acid or an electrolyte mainly containing nitric acid (hereinafter referred to as “nitric acid-based electrolyte”). An A1050 (aluminum purity: 99.5%) equivalent material which can be relatively uniformly surface-roughened by electrolysis is used as a support. It is possible to obtain hundreds of thousands of clear printed matters by appropriately selecting a photosensitive layer applied to the support.

In order to improve the plate wear of a printing plate, a printing plate using an aluminum alloy sheet as a support is subjected to exposure and development using a normal method, followed by a high-temperature heat treatment (burning treatment) to strengthen an image area. The burning treatment is generally performed at 200 to 290° C. for 3 to 9 minutes. An aluminum alloy sheet used as a support is required to exhibit heat resistance (burning resistance) which maintains the strength of the support during the burning treatment.

In recent years, the printing speed has increased along with the proceed in printing technology so that stress applied to a printing plate mechanically secured to each side of a plate cylinder of a printer has increased. Therefore, a support having a high strength has been desired. If the strength of the support is insufficient, the secured portion of the support may be deformed or damaged, whereby a printing variation or the like may occur. Accordingly, an increase in strength of the support is indispensable together with the burning resistance.

In order to satisfy such a demand, an aluminum alloy support of which the components are adjusted based on an A1050 equivalent material has been proposed (see JP-A-2005-15912, for example). An attempt has been made which adjusts the components based on an A1050 equivalent material and adjusts the depth of oil pits in the sheet surface in order to satisfy the above demand (JP-A-2004-35936).

DISCLOSURE OF THE INVENTION

In order to further improve the above-mentioned aluminum alloy support, the inventors of the present invention have utilized an aluminum alloy support based on an A1050 equivalent material and conducted studies on the relationship between the surface properties of a cold-rolled sheet and etch pits obtained by the electrolytic surface-roughening treatment. As a result, the inventors have found that an aluminum powder remaining on the surface of the rolled sheet affects etch pit formation, and a uniform pit pattern is obtained by limiting the amount of aluminum powder.

The present invention has been achieved as a result of further experiments and studies based on the above findings. An object of the present invention is to provide an aluminum alloy sheet for a lithographic printing plate which allows pits to be more uniformly formed by an electrochemical surface-roughening treatment, exhibits more excellent adhesion to a photosensitive film and water retention properties, and shows excellent thermal softening resistance (burning resistance), and a method of producing the same.

In order to achieve the above object, an aluminum alloy sheet for a lithographic printing plate according to claim 1 comprises 0.1 to 1.5% of Mg, 0.5% or less of Zn, 0.1 to 0.6% of Fe, 0.03 to 0.15% of Si, 0.0001 to 0.1% of Cu, and 0.0001 to 0.1% of Ti, with the balance being aluminum and impurities, the amount of aluminum powder on the surface of the aluminum alloy sheet being 0.1 to 3.0 mg/m².

An aluminum alloy sheet for a lithographic printing plate according to claim 2 comprises 0.1 to 1.5% of Mg, more than 0.05% and 0.5% or less of Zn, 0.1 to 0.6% of Fe, 0.03 to 0.15% of Si, 0.0001 to 0.10% of Cu, and 0.0001 to 0.05% of Ti, with the balance being aluminum and impurities, the Mg content and the Zn content of the aluminum alloy sheet satisfying a relationship “4×Zn %−1.4%≦Mg %≦4×Zn %+0.6%”, and the amount of aluminum powder on the surface of the aluminum alloy sheet being 0.1 to 3.0 mg/m².

In the aluminum alloy sheet according to claim 2, precipitates with a diameter (circle equivalent diameter) of 0.1 to 1.0 μm are dispersed on the surface of the aluminum alloy sheet in a number of 10,000 to 100,000 per square millimeter (mm²).

In the aluminum alloy sheet according to claim 2 or 3, the quantity of Fe in solid solution (the amount of Fe dissolved) in the aluminum alloy sheet is 20 to 100 ppm.

In the aluminum alloy sheet according to any one of claims 2 to 4, some or all of the elements of the aluminum alloy sheet form intermetallic compounds, the content of Fe which forms an intermetallic compound is 50 to 99.8% of the total Fe content, the content of Si which forms an intermetallic compound is 5 to 40% of the total Si content, and the ratio (B %/A %) of the content (B %) of Fe which forms an Al—Fe—Si intermetallic compound to the content (A %) of Fe which forms an Al—Fe intermetallic compound is 0.9 or less.

In the aluminum alloy sheet according to any one of claims 1 to 5, the number of oil pits with a diameter (circle equivalent diameter) of 30 μm or more formed in the surface of the aluminum alloy sheet is 50 or less per square millimeter (mm²).

The aluminum alloy sheet according to any one of claims 1 to 6 further comprises more than 0.05% and 0.3% or less of Mn.

In the aluminum alloy sheet according to any one of claims 1 to 7, the average grain size of the aluminum alloy sheet in a direction perpendicular to a rolling direction with respect to the surface of the aluminum alloy sheet is 100 μm or less, and the average grain size in a direction parallel to the rolling direction with respect to the surface of the aluminum alloy sheet is 2 to 20 times the average grain size in the direction perpendicular to the rolling direction.

The aluminum alloy sheet according to any one of claims 1 to 8 further comprises one or more elements selected from Pb, In, Sn, and Ga in an amount of 0.005 to 0.05% in total.

The aluminum alloy sheet according to any one of claims 3 to 9 has a 0.2% proof stress of 120 MPa or more after being subjected to a heat treatment at 270° C. for seven minutes.

A method of producing an aluminum alloy sheet for a lithographic printing plate according to claim 11 comprises casting an aluminum alloy having the composition according to any one of claims 2, 7, and 9 to obtain an ingot, scalping a rolling-side surface of the ingot by 3 to 15 mm, subjecting the ingot to a homogenization treatment which includes heating the ingot to 450 to 580° C. at a temperature increase rate of 20 to 60° C./hr and keeping the ingot at 450 to 580° C. for one hour or more, hot-rolling the resulting product to a thickness of 5 mm or less under conditions where the hot rolling start temperature is 400 to 520° C. and the hot rolling finish temperature is 320 to 400° C., and cold-rolling the hot-rolled product without subjecting the hot-rolled product to process annealing.

A method of producing an aluminum alloy sheet for a lithographic printing plate according to claim 12 comprises casting an aluminum alloy having the composition according to any one of claims 2, 7, and 9 to obtain an ingot, scalping a rolling-side surface of the ingot by 3 to 15 mm, subjecting the ingot to a homogenization treatment which includes heating the ingot to 450 to 580° C. at a temperature increase rate of 20 to 60° C./hr and keeping the ingot at 450 to 580° C. for one hour or more, cooling the resulting product to room temperature, heating the cooled product to 350 to 500° C. and hot-rolling the product to a thickness of 5 mm or less under conditions where the hot rolling finish temperature is 300 to 380° C., and cold-rolling the hot-rolled product without subjecting the hot-rolled product to process annealing.

A method of producing an aluminum alloy sheet for a lithographic printing plate according to claim 13 comprises casting an aluminum alloy having the composition according to any one of claims 2, 7, and 9 to obtain an ingot, scalping a rolling-side surface of the ingot by 3 to 15 mm, subjecting the ingot to a homogenization treatment which includes heating the ingot to 450 to 580° C. and keeping the ingot at 450 to 580° C. for three hours or more, cooling the resulting product subjected to the homogenization treatment to a hot rolling start temperature at a temperature decrease rate of 20 to 60° C./hr, hot-rolling the cooled product to a thickness of 5 mm or less under conditions where the hot rolling start temperature is 400 to 500° C. and the hot rolling finish temperature is 300 to 400° C., and cold-rolling the hot-rolled product without subjecting the hot-rolled product to process annealing.

A method of producing the aluminum alloy sheet according to claim 14 is a method of producing the aluminum alloy sheet according to claim 1 or 2, the method comprising subjecting the aluminum alloy sheet to final cold rolling using a rolling oil with a viscosity of 1 to 6 cSt.

A method of producing the aluminum alloy sheet according to claim 15 is a method of producing the aluminum alloy sheet according to claim 1 or 2, the method comprising subjecting the aluminum alloy sheet to final cold rolling using a rolling oil, the Mg content (Mg %) of the aluminum alloy sheet and the viscosity p of the rolling oil satisfying a relationship “−2×Mg %+2≦ρ≦−2×Mg %+8”.

A method of producing the aluminum alloy sheet according to claim 16 is a method of producing the aluminum alloy sheet according to claim 6, the method comprising subjecting the aluminum alloy sheet to final cold rolling using a roll having a roll surface with an arithmetic average roughness Ra of 0.2 to 0.5 μm and a rolling oil with a viscosity of 1 to 6 cSt.

A method of producing the aluminum alloy sheet according to claim 17 is a method of producing the aluminum alloy sheet according to claim 6, the method comprising subjecting the aluminum alloy sheet to final cold rolling using a rolling oil, the Mg content (Mg %) of the aluminum alloy sheet and the viscosity p of the rolling oil satisfying a relationship “ρ≦2×Mg+4”.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart showing a wiping method for measuring the amount of aluminum powder.

FIG. 2 is a flowchart showing a phenol residue analysis method for measuring the Fe content and the Si content of intermetallic compounds.

BEST MODE FOR CARRYING OUT THE INVENTION

The meanings and the reasons relating to the limitations on the alloy components of the aluminum alloy sheet for a lithographic printing plate according to the present invention are given below. Specifically, most Mg is dissolved in aluminum to improve strength and thermal softening resistance. The term “strength” used herein refers to the tensile strength of a printing plate support at room temperature. The strength is preferably 160 MPa or more in practical applications. The term “thermal softening resistance” used herein is also called burning resistance, and refers to 0.2% proof stress after heating at about 280° C. The thermal softening resistance is preferably 90 MPa or more in practical applications. The Mg content is preferably 0.1 to 1.5%. If the Mg content is less than 0.1%, Mg may not exhibit a sufficient effect. If the Mg content exceeds 1.5%, the uniformity of pits obtained by the surface-roughening treatment may decrease, whereby a non-image area may easily become dirty.

Most Zn is dissolved in aluminum in the same manner as Mg. On the other hand, Zn does not improve strength and thermal softening resistance, but affects an oxide film formed on the surface of aluminum. The oxide film formed on the surface of aluminum is classified as an oxide film formed when allowed to stand at room temperature (spontaneous oxide film) and an oxide film formed during a heat treatment performed in the production process. Zn affects both of these oxide films.

Specifically, an aluminum alloy containing Mg tends to produce an oxide film mainly formed of an Mg oxide (MgO) during a heat treatment such as heating during homogenization or hot rolling or process annealing. Since such an oxide film is active and porous, wettability with a treatment liquid is improved during the electrolytic surface-roughening treatment so that surface roughening is promoted. On the other hand, pits tend to become non-uniform. Zn improves non-uniformity of the surface-roughened structure, and suppresses activation due to the Mg oxide. The Zn content is preferably 0.5% or less. If the Zn content exceeds 0.5%, an effect of suppressing activation due to the Mg oxide may increase so that surface roughening may become non-uniform. Moreover, since coarse intermetallic compounds tend to be produced, large pits may be formed during the electrolytic treatment, whereby surface-roughening uniformity may be further impaired. The Zn content is more preferably more than 0.05% and 0.5% or less, and still more preferably 0.06 to 0.5%.

Fe produces Al—Fe intermetallic compounds, and produces Al—Fe—Si intermetallic compounds together with Si. These compounds are dispersed to refine the recrystallization structure. Pits are uniformly formed from these compounds as starting points and are finely distributed during the electrolytic treatment. The Fe content is preferably 0.1 to 0.6%. If the Fe content is less than 0.1%, the distribution of the compounds may become non-uniform so that an unetched area may occur during the electrolytic treatment. As a result, formation of pits may become non-uniform. If the Fe content exceeds 0.6%, coarse compounds may be produced, whereby the uniformity of the surface-roughened structure may decrease.

Si produces Al—Fe—Si intermetallic compounds together with Fe. These compounds are dispersed to refine the recrystallization structure. Pits are uniformly formed from these compounds as starting points and are finely distributed during the electrolytic treatment. The Si content is preferably 0.03 to 0.15%. If the Fe content is less than 0.03%, the distribution of the compounds may become non-uniform so that an unetched area may occur during the electrolytic treatment. As a result, formation of pits may become non-uniform. If the Si content exceeds 0.15%, coarse compounds may be produced. Moreover, precipitation of Si tends to occur, whereby the uniformity of the surface-roughened structure may decrease.

Cu is easily dissolved in aluminum. When the Cu content is 0.0001 to 0.10%, Cu exhibits a pit refinement effect. If the Cu content exceeds 0.10%, pits may become large and non-uniform during the electrolytic treatment, and an unetched area may occur. In the present invention, the amount of Cu mixed from an ingot employed to obtain the above Fe content and Si content is about 5 to 100 ppm (0.0005 to 0.01%).

Ti refines an ingot structure and crystal grains. As a result, Ti makes formation of pits uniform during the electrolytic treatment to prevent occurrence of streaks during printing using the resulting printing plate. The Ti content is preferably 0.0001 to 0.05%. If the Ti content is less than 0.0001%, Ti may not exhibit a sufficient effect. If the Ti content exceeds 0.05%, coarse Al—Ti compounds may be produced, whereby the surface-roughened structure tends to become non-uniform. When adding B together with Ti in order to refine the ingot structure, the Ti content is preferably 0.01% or less.

Mn increases strength and thermal softening resistance. The Mn content is preferably more than 0.05% and 0.3% or less. If the Mn content is less than 0.05%, Mn may not exhibit a sufficient effect. If the Mn content exceeds 0.3%, coarse Al—Fe—Mn compounds or Al—Fe—Mn—Si compounds may be easily produced, whereby surface roughening during the electrolytic treatment may become non-uniform. The Mn content is more preferably 0.06 to 0.3%.

In the aluminum alloy sheet for a lithographic printing plate according to the present invention, the Mg content and the Zn content preferably satisfy the relationship “4%×Zn %−1.4%≦Mg %≦4×Zn %+0.6%”. If the Mg content and the Zn content satisfy this relationship, formation of pits during the electrolytic treatment becomes more uniform so that an excellent surface-roughened structure can be obtained. If 4×Zn %−1.4%>Mg %, since the Zn content is in excess with respect to the Mg content, an effect of suppressing activation of the Mg oxide increases, whereby formation of pits during the electrolytic treatment may become non-uniform. As a result, formation of a roughened surface may become non-uniform. If Mg %>4×Zn %+0.6%, since the Mg content is in excess with respect to the Zn content, an effect of suppressing activation of the Mg oxide decreases, whereby formation of pits during the electrolytic treatment may become non-uniform. As a result, formation of a roughened surface may become non-uniform.

The aluminum alloy sheet for a lithographic printing plate according to the present invention exhibits improved electrolytic graining properties by adding one or more of Pb, In, Sn, and Ga in an amount of 0.005 to 0.05% in total. Therefore, a desired pit pattern can be obtained with a small amount of electricity. If the total amount of one or more elements selected from the group consisting of Pb, In, Sn, and Ga is less than 0.005%, the effect of addition may be insufficient. If the total amount of one or more elements selected from the group consisting of Pb, In, Sn, and Ga exceeds 0.05%, the shape of pits may be deformed.

The aluminum alloy sheet for a lithographic printing plate according to the present invention is produced by casting the above aluminum alloy by continuous casting or the like to obtain an ingot, homogenizing the resulting ingot, hot-rolling the homogenized product, and cold-rolling the hot-rolled product. It is important to adjust the amount of aluminum powder on the surface of the rolled sheet after final cold rolling to 0.1 to 3.0 mg/m². The term “aluminum powder” used herein refers to an aluminum alloy powder which is produced from the aluminum alloy rolled sheet during final cold rolling and remains on the surface of the rolled sheet. In the aluminum alloy according to the present invention which contains Mg, if the amount of aluminum powder is less than 0.1 mg/m², an effect of preventing abrasion of a coil may be insufficient when the rolled sheet is wound as a coil after final cold rolling. If the amount of aluminum powder exceeds 3.0 mg/m², the aluminum powder may not be removed sufficiently during a degreasing process and remain on the surface of the sheet, whereby formation of pits may become insufficient or non-uniform in the area in which the aluminum powder remains during the electrolytic surface-roughening treatment, and an inferior appearance due to an unetched area or an irregular pattern may occur after electrolytic graining. Moreover, an excessive aluminum powder may contaminate the production line.

In order to adjust the amount of aluminum powder on the surface of the sheet after final cold rolling to the above range, it is necessary to adjust the degree of final cold rolling, the properties of the rolling oil, and the amount of rolling oil supplied depending on the composition in addition to adjusting the components. In particular, the viscosity of the rolling oil used for final cold rolling is important. It is preferable to use a rolling oil with a viscosity of 1 to 6 cSt. If the viscosity is less than 1 cSt, since the amount of rolling oil introduced between the roll and the rolled sheet decreases, a lubrication failure occurs, whereby a large amount of aluminum powder tends to be produced. If the viscosity exceeds 6 cSt, since the amount of rolling oil introduced between the roll and the rolled sheet increases to a large extent, the amount of aluminum powder produced tends to decrease.

If the Mg content (Mg %) of the aluminum alloy and the viscosity p of the rolling oil used for final cold rolling have the relationship (−2×Mg %+2)>ρ, deformation resistance decreases and the amount of rolling oil introduced between the roll and the rolled sheet decreases, whereby a large amount of aluminum powder tends to be produced. If ρ>(−2×Mg %+8), since the amount of rolling oil introduced between the roll and the rolled sheet increases to a large extent, the amount of aluminum powder produced tends to decrease.

In the present invention, when precipitates with a diameter (circle equivalent diameter) of 0.1 to 1.0 μm are dispersed on the surface of the sheet in a number of 10,000 to 100,000 per square millimeter (mm²), more uniform etch pits can be formed during the electrolytic treatment. If the number of precipitates is less than 10,000 per square millimeter, an unetched area tends to occur, whereby a number of large pits may be formed. If the number of precipitates exceeds 100,000 per square millimeter, it may be difficult to form uniform pits, thereby making it difficult to obtain an aluminum alloy sheet suitable as a lithographic printing support.

In the present invention, burning resistance can be maintained by setting the quantity of Fe in solid solution at 20 to 100 ppm so that uniform etch pits can be formed by the electrolytic treatment. If the amount of Fe dissolved is less than 20 ppm, burning resistance tends to decrease. If the amount of Fe dissolved exceeds 100 ppm, the pit pattern becomes non-uniform due a decrease in electrolytic surface-roughening properties. This makes it difficult to obtain an aluminum alloy sheet suitable as a lithographic printing support.

More uniform pits can be formed by the electrolytic treatment when some or all of the elements of the aluminum alloy sheet according to the present invention form intermetallic compounds, the content of Fe which forms an intermetallic compound is 50 to 99.8% of the total Fe content, the content of Si which forms an intermetallic compound is 5 to 40% of the total Si content, and the ratio (B %/A %) of the content (B %) of Fe which forms an Al—Fe—Si intermetallic compound to the content (A %) of Fe which forms an Al—Fe intermetallic compound is 0.9 or less.

If the content of Fe which forms an intermetallic compound is less than 50% of the total Fe content, since a sufficient number of intermetallic compounds as pit starting points may not be obtained, large pits tend to be formed. If the content of Fe which forms an intermetallic compound exceeds 99.8% of the total Fe content, since a large number of intermetallic compounds are produced, it may be difficult to obtain a uniform pit pattern. If the content of Si which forms an intermetallic compound is less than 5% of the total Si content, since the amount of Si dissolved increases, the potential difference between the matrix and the intermetallic compound decreases, whereby electrochemical solubility decreases. Moreover, precipitation of Si occurs to a large extent, whereby ink contamination tends to occur. If the content of Si which forms an intermetallic compound exceeds 40% of the total Si content, since a large number of intermetallic compounds are produced, it may be difficult to obtain a uniform pit pattern.

The Al—Fe intermetallic compound has an electrochemical solubility higher than that of the Al—Fe—Si intermetallic compound to more positively act as a pit starting point as compared with the Al—Fe—Si intermetallic compound. If the ratio (B %/A %) of the content (B %) of Fe which forms the Al—Fe—Si intermetallic compound to the content (A %) of Fe which forms the Al—Fe intermetallic compound is larger than 0.9, since pit formation efficiency decreases, large pits tend to be formed.

In the present invention, etch pits formed by the electrolytic surface-roughening treatment can be made more uniform by adjusting the number of oil pits with a diameter (circle equivalent diameter) of 30 μm or more formed in the surface of the aluminum alloy sheet after final cold rolling to 50 or less per square millimeter (mm²). Since the aluminum alloy according to the present invention contains Mg, large oil pit with a diameter of 30 μm or more tend to remain as large pits after electrolytic graining. If the number of such large pits exceeds 50 per square millimeter (mm²), etch pits formed by the electrolytic surface-roughening treatment tend to become non-uniform.

In order to adjust the number of oil pits with a diameter (circle equivalent diameter) of 30 μm or more to 50 or less per square millimeter (mm²), it is necessary to adjust the degree of final cold rolling, the configuration of the roll, the properties of the rolling oil, and the amount of rolling oil supplied. When using an aluminum alloy which contains Mg and has a relatively high deformation resistance as that of the aluminum alloy according to the present invention, it is preferable to use a roll having a roll surface with an arithmetic average roughness Ra of 0.2 to 0.5 μm during final cold rolling and to perform cold rolling using a rolling oil with a viscosity of 1 to 6 cSt.

If the roll surface has an arithmetic average roughness Ra exceeding 0.5 μm, the oil film breaks due to an increase in local contact pressure in the contact arc length, whereby the metal contact area increases. As a result, a lubrication failure tends to occur. If the arithmetic average roughness Ra is less than 0.2 μm, since the amount of rolling oil introduced between the roll and the rolled sheet increases to a large extent, the number of large oil pits may increase. If the viscosity of the rolling oil is less than 1 cSt, since the amount of rolling oil introduced between the roll and the rolled sheet decreases, a lubrication failure occurs. If the viscosity of the rolling oil exceeds 6 cSt, since the amount of rolling oil introduced between the roll and the rolled sheet increases to a large extent, the number of large oil pits may increase.

As the rolling oil used during final cold rolling, it is preferable to use a rolling oil which ensures that the Mg content (Mg %) of the aluminum alloy sheet and the viscosity ρ of the rolling oil satisfy the relationship “ρ≦2×Mg+4”. If ρ>(2×Mg+4), deformation resistance decreases. Moreover, since the amount of rolling oil introduced between the roll and the rolled sheet increases, a number of large pits tend to be formed.

In the present invention, occurrence of an inferior appearance after electrolytic graining due to irregular surface quality and streaks can be suppressed by specifying the grain size with respect to the surface of the sheet. Specifically, the average grain size in the direction perpendicular to the rolling direction with respect to the surface of the sheet is adjusted to be 100 μm or less, and the average grain size in the direction parallel to the rolling direction with respect to the surface of the sheet is adjusted to be 2 to 20 times the average grain size in the direction perpendicular to the rolling direction. If the average grain size in the direction perpendicular to the rolling direction with respect to the surface of the sheet exceeds 100 μm, the surface quality may become irregular. If the average grain size in the direction parallel to the rolling direction with respect to the surface of the sheet is less than twice the average grain size in the direction perpendicular to the rolling direction, the strength necessary for a printing plate support may not be obtained. If the average grain size in the direction parallel to the rolling direction with respect to the surface of the sheet is more than 20 times the average grain size in the direction perpendicular to the rolling direction, streaks may occur.

The aluminum alloy sheet for a lithographic printing plate according to the present invention is produced by casting the above aluminum alloy by continuous casting or the like to obtain an ingot, homogenizing the resulting ingot, hot-rolling the homogenized product, and cold-rolling the hot-rolled product.

It is preferable to face each rolling-side surface of the ingot by 3 to 15 mm. If the amount of scalping is less than 3 mm per side, since coarse crystal grains (coarse crystal) in the vicinity of the ingot surface may be removed to only a small extent, the faced surface may have a non-uniform structure, whereby streaks may occur. If the amount of scalping exceeds 15 mm per side, economic efficiency may be impaired due to a decrease in yield.

When producing the aluminum alloy sheet in which precipitates with a diameter (circle equivalent diameter) of 0.1 to 1.0 μm are dispersed on the surface of the sheet in a number of 10,000 to 100,000 per square millimeter (mm²), the operation from the ingot homogenization treatment to hot rolling is preferably carried out as follows.

The temperature increase rate of the ingot during the homogenization treatment is preferably 20 to 60° C./hr. This is effective to obtain the above precipitate distribution. If the temperature increase rate is less than 20° C./hr, precipitation proceeds so that the diameter of the precipitate tends to exceed 1 μm and the number of precipitates decreases. Moreover, economic efficiency may be impaired since heating requires time. If the temperature increase rate exceeds 60° C./hr, it is difficult to obtain specific precipitates since precipitation does not proceed due to too high a temperature increase rate.

The homogenization treatment is preferably performed at 450 to 580° C. for one hour or more. The homogenization treatment causes Fe and Si which have been dissolved to supersaturation to uniformly precipitate. As a result, etch pits formed during the electrolytic treatment have a minute circular shape, whereby plate wear is improved. If the homogenization treatment temperature is less than 450° C., precipitation of Fe and Si which serve as pit starting points may be insufficient so that an unetched area may be formed during the electrolytic treatment. As a result, the pit pattern may become non-uniform. If the homogenization treatment temperature exceeds 580° C., since the quantity of Fe in solid solution increases, the number of minute precipitates which serve as pit starting points decreases. If the homogenization treatment time is less than one hour, precipitation of Fe and Si becomes insufficient, whereby the pit pattern may become non-uniform.

The hot rolling start temperature is preferably 400 to 520° C. If the hot rolling start temperature is less than 400° C., precipitation of Fe and Si which serve as pit starting points may be insufficient so that an unetched area may be formed during the electrolytic treatment. As a result, the pit pattern may become non-uniform. Moreover, since the degree of rolling cannot be increased due to an increase in deformation resistance, the number of rolling passes increases, whereby economic efficiency may be impaired. If the hot rolling start temperature exceeds 520° C., since coarse recrystallized grains are produced during hot rolling, streaks tend to occur due to the streak-shaped non-uniform structure.

The hot rolling finish temperature is preferably 320 to 400° C. If the hot rolling finish temperature is less than 320° C., recrystallization may occur only partially, whereby an unrecrystallized area may cause streaks. Moreover, since the amount of strain accumulated after final cold rolling may increase, the recrystallizing temperature may decrease, whereby burning resistance may decrease. If the hot rolling finish temperature exceeds 400° C., recrystallization occurs over the entire surface. However, since coarse crystal grains are produced, streaks may occur. The thickness of the sheet when finishing hot rolling is preferably 5 mm or less. If the thickness of the sheet when finishing hot rolling is 5 mm or more, the rolling rate during hot rolling may become insufficient so that the amount of strain introduced may decrease, whereby recrystallized grains may become coarse.

When producing the aluminum alloy sheet in which the quantity of Fe in solid solution is adjusted to 20 to 100 ppm, the operation from the ingot homogenization treatment to hot rolling is preferably carried out as follows.

The temperature increase rate of the ingot during the homogenization treatment is preferably 20 to 60° C./hr. This is effective to obtain the above specific dissolution state. If the temperature increase rate is less than 20° C./h, the amount of dissolution may decrease to a large extent due to an increase in the amount of precipitation. Moreover, economic efficiency may be impaired since heating requires time. If the temperature increase rate exceeds 60° C./hr, it is difficult to obtain the above specific dissolution state since precipitation does not proceed due to too high a temperature increase rate.

The homogenization treatment is preferably performed at 450 to 580° C. for one hour or more. By the homogenization treatment, Fe and Si which have been dissolved to supersaturation, are uniformly and minutely precipitated. As a result, etch pits formed during the electrolytic treatment have a minute circular shape, whereby plate wear is improved. If the homogenization treatment temperature is less than 450° C., precipitation of Fe and Si (i.e., a reduction in the quantity of Fe and Si in solid solution) may be insufficient. As a result, the pit pattern may become non-uniform. If the homogenization treatment temperature exceeds 580° C., since the quantity of Fe in solid solution may increase to a large extent, the pit pattern may become non-uniform. If the homogenization treatment time is less than one hour, the dissolution state of Fe and Si in the longitudinal direction and the width direction becomes non-uniform, whereby the pit pattern may become non-uniform.

It is possible to control precipitation of Fe and Si by decreasing the temperature to room temperature after the homogenization treatment, whereby the desired dissolution state can be obtained.

The hot rolling start temperature is preferably 350 to 500° C. If the hot rolling start temperature is less than 350° C., since the degree of rolling cannot be increased due to an increase in deformation resistance, the number of rolling passes increases, whereby economic efficiency may be impaired. If the hot rolling start temperature exceeds 500° C., since coarse recrystallized grains are produced during hot rolling, streaks tend to occur due to the streak-shaped non-uniform structure.

The hot rolling finish temperature is preferably 300 to 380° C. If the hot rolling finish temperature is less than 300° C., recrystallization may occur only partially, whereby an unrecrystallized area may cause streaks. Moreover, since the amount of strain accumulated after final cold rolling may increase, the recrystallizing temperature may decrease, whereby burning resistance may decrease. If the hot rolling finish temperature exceeds 380° C., recrystallization occurs over the entire surface. However, since coarse crystal grains are produced, streaks may occur. The thickness of the sheet when finishing hot rolling is preferably 5 mm or less. If the thickness of the sheet when finishing hot rolling is 5 mm or more, the rolling rate during hot rolling may become insufficient so that the amount of strain introduced may decrease, whereby recrystallized grains may become coarse.

When producing the aluminum alloy sheet in which some or all of the elements of the aluminum alloy sheet form intermetallic compounds, the content of Fe which forms an intermetallic compound is 50 to 99.8% of the total Fe content, the content of Si which forms an intermetallic compound is 5 to 40% of the total Si content, and the ratio (B %/A %) of the content (B %) of Fe which forms an Al—Fe—Si intermetallic compound to the content (A %) of Fe which forms an Al—Fe intermetallic compound is 0.9 or less, the operation from the ingot homogenization treatment to hot rolling is preferably carried out as follows.

The homogenization treatment is preferably performed at 450 to 580° C. for three hours or more. The homogenization treatment causes Fe and Si which have been dissolved to supersaturation to uniformly precipitate. As a result, etch pits formed during the electrolytic treatment have a minute circular shape, whereby plate wear is improved. If the homogenization treatment temperature is less than 450° C., precipitation of Al—Fe—Si intermetallic compounds which serve as pit starting points to only a small extent may proceed so that large pits may be formed due to a decrease in pit formation efficiency. As a result, the pit pattern may become non-uniform. If the homogenization treatment temperature exceeds 580° C., since the quantity of Fe in solid solution increases, precipitation of Al—Fe intermetallic compounds which serve as pit starting points to a large extent decreases. If the homogenization treatment time is less than three hours, precipitation of Fe and Si becomes insufficient, whereby the pit pattern may become non-uniform.

It is preferable to decrease the temperature of the ingot to the hot rolling start temperature at a temperature decrease rate of 20 to 60° C./hr after the homogenization treatment, and to start hot rolling at 400 to 500° C. Precipitation proceeds when decreasing the temperature of the ingot after the homogenization treatment. In particular, precipitation of not only Fe but also Si proceeds when decreasing the temperature of the ingot to 400 to 450° C. If the temperature decrease rate is less than 20° C./hr, precipitation of Al—Fe—Si intermetallic compounds proceeds to a large extent. When precipitation proceeds further, the diameter of the precipitate may exceed 1 μm and the number of precipitates decreases. Moreover, economic efficiency may be impaired since heating requires time. If the temperature decrease rate exceeds 60° C./hr, the period of time for precipitation may be insufficient. Moreover, since the temperature of the ingot may become non-uniform, precipitation of Fe and Si also may become non-uniform. As a result, recrystallization during the subsequent hot rolling may become non-uniform, whereby streaks tend to occur.

The hot rolling start temperature is preferably 400 to 500° C. If the hot rolling start temperature is less than 400° C., since the degree of rolling cannot be increased due to an increase in deformation resistance, the number of rolling passes increases, whereby economic efficiency may be impaired. If the hot rolling start temperature exceeds 500° C., since coarse recrystallized grains are produced during hot rolling, streaks tend to occur due to the streak-shaped non-uniform structure.

The hot rolling finish temperature is preferably 300 to 400° C. If the hot rolling finish temperature is less than 300° C., recrystallization may occur only partially, whereby an unrecrystallized area may cause streaks. Moreover, since the amount of strain accumulated after final cold rolling may increase, the recrystallizing temperature may decrease, whereby burning resistance may decrease. If the hot rolling finish temperature exceeds 400° C., recrystallization occurs over the entire surface. However, since coarse crystal grains are produced, an irregular pattern or streaks may occur. The thickness of the sheet when finishing hot rolling is preferably 5 mm or less. If the thickness of the sheet when finishing hot rolling is 5 mm or more, the rolling rate during hot rolling may become insufficient so that the amount of strain introduced may decrease, whereby recrystallized grains may become coarse.

The aluminum alloy sheet subjected to hot rolling as described above is cold-rolled without being subjected to process annealing. Cold rolling is performed after hot rolling in order to provide a strength which prevents breakage when winding a support around a plate cylinder and adjusting the length of crystal grains produced during hot rolling or immediately after hot rolling in the direction parallel to the rolling direction when applying the aluminum alloy sheet as a lithographic printing support. The degree of rolling is preferably 50 to 98%. If the degree of rolling is less than 50%, it is difficult to provide a strength which prevents breakage when winding the support around a plate cylinder. If the degree of rolling exceeds 98%, crystal grains produced after hot rolling extend to a large extent along the direction parallel to the rolling direction, whereby streaks tend to occur. After cold rolling, finish cold rolling may be performed using a roll provided with a special pattern on the surface to obtain an aluminum alloy sheet having a surface roughness indicated by an arithmetic average roughness Ra of 0.15 to 0.30 μm, an average elevation/depression dimension RSm of 50 μm or less in the direction perpendicular to the rolling direction, a maximum depression depth Rv of 1 μm or less, and a maximum height Rz of 1.5 to 2.5 μm.

The amount of aluminum powder on the surface of the sheet, the precipitate distribution, the quantity of Fe in solid solution, the relationship between the intermetallic compounds and the Fe content and the Si content, the oil pit distribution, and the crystal grain size as specified above are obtained by combining the above composition and production steps, whereby a 0.2% proof stress after a heat treatment at 270° C. for seven minutes of 120 MPa or more is achieved. The above strength properties are important for a printing plate support. If the 0.2% proof stress is less than 120 MPa, the secured portion of the printing plate may be deformed or damaged during printing, whereby incorrect printing or the like may occur.

EXAMPLES

Examples according to the present invention are described below in contrast with comparison examples to demonstrate the effects of the present invention. Note that these examples illustrate only preferred embodiments of the present invention. The present invention is not limited to these examples.

Example 1 and Comparison Example 1

As a specimen aluminum alloy, an aluminum alloy having a composition shown in Table 1 was melted and cast. Each rolling side of the resulting ingot was faced by 5 mm to reduced to the thickness of the ingot to 500 mm. The ingot was heated to 530° C. at a temperature increase rate of 35° C./hr. The ingot was then subjected to homogenization at 530° C. for 3.5 hours.

The temperature of the ingot was decreased to 515° C. (hot rolling start temperature) at a temperature decrease rate of 35° C./hr from the homogenization treatment temperature (530° C.). The ingot was then hot-rolled to a thickness of 3 mm. Hot rolling was finished at 346° C. The hot-rolled product was cold-rolled to a thickness of 0.3 mm without being subjected to process annealing. The arithmetic average roughness Ra of a roll used for cold rolling was 0.3 μm, and the viscosity of a rolling oil was 3 cSt. In Table 1, a value outside the condition according to the present invention is underlined. A case where the relational equation “(4×Zn %−1.4%)≦Mg %≦(4×Zn %+0.6%)” relating to the Mg content and the Zn content was satisfied is indicated by “Good”, and a case where the relational equation “(4×Zn %−1.4%)≦Mg %≦(4×Zn %+0.6%)” relating to the Mg content and the Zn content was not satisfied is indicated by “Bad”.

The amount of aluminum powder on the surface of the sheet after cold rolling, the number of precipitates with a diameter of 0.1 to 1.0 μm, the number of oil pits with a diameter of 30 μm or more formed in the surface of the sheet, and the crystal grain size of the resulting aluminum alloy sheet (specimen) were measured according to the following methods. The results are shown in Table 2. The burning resistance of the resulting aluminum alloy sheet was evaluated, and the presence or absence of scratches due to rubbing which occurred on a coil wound after cold rolling was observed. The results are shown in Table 3. In Table 2, the term “crystal length” indicates the crystal grain size (GL) in the direction parallel to the rolling direction with respect to the surface of the sheet, the term “crystal width” indicates the crystal grain size (GT) in the direction perpendicular to the rolling direction, and the term “ratio” indicates the ratio (GL/GT) of the crystal grain size (GL) to the crystal grain size (GT). A value outside the condition according to the present invention is underlined.

Measurement of amount of aluminum powder: As a quantitative analysis of residual powder on the surface of the sheet, a specific area of the surface of the sheet was wiped off with an absorbent cotton immersed in a solvent, and the aluminum content of the absorbent cotton was measured. FIG. 1 shows a wiping method.

Measurement of number of precipitates with a diameter (circle equivalent diameter) of 0.1 to 1.0 μm: After degreasing and washing the surface of the aluminum alloy sheet, the surface of the aluminum alloy sheet was etched for 10 seconds using an aqueous solution (Keller's reagent) prepared by mixing nitric acid, hydrofluoric acid, and hydrochloric acid, and was photographed using an optical microscope at a magnification of 1000. The particle diameter distribution of precipitates was measured using an image analyzer (Luzex 500 manufactured by Nireco Corporation). The diameter of the precipitate was converted into the diameter of a circle having the same area as that of the precipitate in the photograph (i.e., circle equivalent diameter), and the intermetallic compound distribution density was determined from the results.

Measurement of number of oil pits: After degreasing and washing the surface of the aluminum alloy sheet, the surface of the aluminum alloy sheet was observed using a scanning electron microscope (SEM) at a magnification of 500. The number of oil pits and their distribution were measured by an intercept method.

Measurement of crystal grain size: After degreasing and washing the surface of the aluminum alloy sheet, the surface of the aluminum alloy sheet was mirror-polished and then anodized using Parker's reagent. The crystal grains were observed in a polarization mode of an optical microscope, and the crystal grain size in the direction perpendicular or parallel to the rolling direction was determined using an intercept method.

Evaluation of burning resistance: As an index of thermal softening resistance, the aluminum sheet was heated in an atmospheric furnace maintained at 270° C. for seven minutes, and was subjected to a tensile test to measure the 0.2% proof stress. The burning resistance of a support was evaluated based on the 0.2% proof stress. The proof stress was measured in the direction (direction L) parallel to the rolling direction of the aluminum alloy sheet. A case where the 0.2% proof stress after heating at 270° C. for seven minutes was 120 MPa or more was evaluated as “Good”, and a case where the 0.2% proof stress was less than 120 MPa was evaluated as “Bad”.

Observation of the presence or absence of coil scratches due to rubbing: A case where scratches due to rubbing were observed in a specific area of the surface of the sheet with the naked eye was evaluated as “Bad”, and a case where scratches due to rubbing were not observed was evaluated as “Good”.

The resulting aluminum alloy sheet was subjected to degreasing (solution: 5% sodium hydroxide, temperature: 60° C., time: 10 seconds), neutralization (solution: 10% nitric acid, temperature: 20° C., time: 30 seconds), an alternating-current electrolytic surface-roughening treatment (solution: 2.0% hydrochloric acid, temperature: 25° C., frequency: 50 Hz, current density: 60 A/dm², time: 20 seconds), a desmut process (solution: 5% sodium hydroxide, temperature: 60° C., time: 5 seconds), and an anodizing process (solution: 30% sulfuric acid, temperature: 20° C., time: 60 seconds). The aluminum alloy sheet was then washed with water, dried, and cut to a specific size to prepare a specimen.

The presence or absence of an irregular pattern and streaks was observed for each specimen. The surface of the specimen was observed using a scanning electron microscope (SEM) at a magnification of 500. The surface of the specimen was photographed so that the field of view was 0.04 mm². Occurrence of an unetched area and uniformity of etch pits were evaluated based on the resulting photograph. The results are shown in Table 3.

Observation of the presence or absence of irregular pattern: A case where a significant irregular pattern was observed on the surface of the specimen with the naked eye was evaluated as “Bad”, a case where no significant irregular pattern was observed was evaluated as “Good”, and a case where no irregular pattern was observed was evaluated as “Excellent”.

Observation of the presence or absence of streaks: A case where streaks were observed on the surface of the specimen with the naked eye was evaluated as “Bad”, and a case where streaks were not observed was evaluated as “Good”.

Evaluation of occurrence of unetched area: A case where the percentage of an unetched area exceeded 20% was evaluated as “Bad”, a case where the percentage of an unetched area was 15 to 20% was evaluated as “Good”, and a case where the percentage of an unetched area was less than 15% was evaluated as “Excellent”.

Evaluation of uniformity of etch pits: A case where the area ratio of large pits with a circle equivalent diameter exceeding 10 μm was more than 10% with respect to all pits was evaluated as “Bad”, a case where the area ratio was 5 to 10% was evaluated as “Good”, and a case where the area ratio was less than 5% was evaluated as “Excellent”.

TABLE 1 Composition (wt %) Pb + Relational In + Alloy Mg Zn Fe Si Cu Ti Mn equation Pb In Sn Ga Sn + Ga Remarks A 0.22 0.110 0.31 0.06 0.0050 0.0130 0.002 Good 0.0002 0.0003 0.0003 0.010 0.0108 Example B 0.13 0.070 0.16 0.03 0.0002 0.0007 0.006 Good 0.0006 0.0006 0.0001 0.013 0.0143 Example C 0.51 0.200 0.28 0.09 0.0021 0.0140 0.080 Good 0.0003 0.0009 0.0004 0.019 0.0206 Example D 1.40 0.120 0.40 0.07 0.0007 0.0053 0.003 Bad 0.0004 0.0002 0.0010 0.014 0.0156 Example E 0.21 0.450 0.33 0.07 0.0009 0.015 0.006 Bad 0.0031 0.0011 0.0011 0.014 0.0193 Example F  0.002  0.0003 0.30 0.06 0.0008 0.0200 0.003 Good 0.0001 0.0016 0.0006 0.017 0.0193 Comparative Example G 2.54 0.490 0.25 0.05 0.0300 0.0310 0.008 Good 0.0015 0.0001 0.0009 0.020 0.0225 Comparative Example H 1.40 0.650 0.31 0.07 0.0011 0.0140 0.003 Good 0.0011 0.0000 0.0008 0.021 0.0229 Comparative Example I 0.12 0.140 0.06 0.01 0.0730 0.0009 0.010 Good 0.0017 0.0004 0.0018 0.016 0.0199 Comparative Example J 0.92 0.310 0.81 0.21 0.0263 0.0072 0.180 Good 0.0005 0.0003 0.0023 0.018 0.0211 Comparative Example K 0.21 0.100 0.30 0.07 0.1500 0.0009 0.180 Good 0.0019 0.0010 0.0007 0.020 0.0236 Comparative Example L 0.67 0.230 0.25 0.13 0.0110 0.1249 0.220 Good 0.0010 0.0005 0.0001 0.017 0.0186 Comparative Example M 1.22 0.420 0.37 0.05 0.0140 0.0101 0.410 Good 0.0005 0.0006 0.00042 0.0009 0.0143 Comparative Example O 1.10 0.39  0.12 0.11 0.0067 0.0005 0.160 Good 0.0089 0.0092 0.0055 0.040 0.0636 Comparative Example

TABLE 2 Number of oil Viscosity Amount of pits with Crystal Crystal ρ of Relationship I Relationship II aluminum diameter of 30 μm length width Ra of roll rolling oil between between powder Precipitate or more GL GT Ratio Specimen Alloy (μm) (cSt) Mg and ρ Mg and ρ mg/m² (/mm²) (/mm²) (μm) (μm) GL/GT 1 A 0.3 3 Good Good 2.50 65520 40 678 68 10.0 2 B 0.3 3 Good Good 2.80 28040 45 810 79 10.3 3 C 0.3 3 Good Good 2.01 73000 35 649 64 10.1 4 D 0.3 3 Good Good 0.12 67860 8 676 63 10.7 5 E 0.3 3 Good Good 2.62 71150 38 667 70 9.5 6 F 0.3 3 Bad Good 4.02 62660 75 729 77 9.5 7 G 0.3 3 Bad Good 0.02 60100 2 740 70 10.6 8 H 0.3 3 Good Good 0.25 60000 10 730 70 10.4 9 I 0.3 3 Good Good 3.06  6980 46 1200 123  9.8 10 J 0.3 3 Good Good 1.08 159980  21 552 51 10.8 11 K 0.3 3 Good Good 2.39 66250 42 675 62 10.9 12 L 0.3 3 Good Good 1.67 57700 33 613 59 10.4 13 M 0.3 3 Good Good 0.70 80310 20 580 57 10.2 14 O 0.3 3 Good Good 2.30 60070 30 1110 93 11.9 Note: Relationship I between Mg and ρ: −2 × Mg % + 2 ≦ ρ ≦ −2 × Mg % + 8 (satisfied: Good, not satisfied: Bad) Relationship II between Mg and ρ: ρ ≦ 2 × Mg % + 4 (satisfied: Good, not satisfied: Bad)

TABLE 3 Burning resistance Specimen (MPa) Scratch Unetched area Pit uniformity Irregular pattern Streaks 1 149 Good Excellent Excellent Good Good 2 130 Good Excellent Excellent Good Good 3 170 Good Excellent Excellent Good Good 4 226 Good Good Good Good Good 5 140 Good Good Good Good Good 6 85 Good Bad Bad Bad Good 7 241 Bad Good Bad Good Good 8 220 Good Good Bad Good Good 9 98 Good Bad Bad Bad Good 10 219 Good Good Bad Good Good 11 148 Good Bad Bad Good Good 12 183 Good Good Bad Good Good 13 209 Good Good Bad Good Good 14 175 Good Good Bad Good Good

As shown in Table 3, specimens No. 1 to No. 5 according to the present invention did not show scratches due to rubbing, exhibited excellent burning resistance, did not produce an irregular pattern and streaks, exhibited excellent etching properties after the electrolytic treatment, and had uniform etch pits over the entire surface.

On the other hand, specimen No. 6 exhibited inferior burning resistance due to low Mg content. Moreover, the amount of aluminum powder increased, and formation of pits became non-uniform. An inferior appearance due to an unetched area and an irregular pattern occurred after electrolytic graining. Specimen No. 7 exhibited inferior pit uniformity due to high Mg content. Moreover, the amount of aluminum powder decreased, and coil scratches due to rubbing occurred. Specimen No. 8 was non-uniformly surface-roughened due to high Zn content. Specimen No. 9 had a small number of precipitates due to low Fe content and low Si content. The distribution of Al—Fe intermetallic compounds and Al—Fe—Si intermetallic compounds became non-uniform, whereby formation of pits became non-uniform. Moreover, the amount of precipitation and the amount of dissolution decreased due to low Fe content, resulting in insufficient burning resistance. Specimen No. 10 produced a large number of precipitates due to high Fe content and high Si content to produce coarse compounds. Therefore, uniformity of the surface-roughened structure decreased. In specimen No. 11, pits became large and non-uniform and an unetched area occurred during the electrolytic treatment due to high Cu content. Specimen No. 12 produced coarse Al—Ti compounds due to high Ti content, whereby the surface-roughened structure became non-uniform. Specimen No. 13 produced coarse Al—Fe—Mn compounds or Al—Fe—Mn—Si compounds due to high Mn content, whereby surface roughening during the electrolytic treatment became non-uniform. In specimen No. 14, the shape of pits was deformed and became non-uniform since the total amount of Pb, In, Sn, and Ga exceeded 0.05%.

Example 2 and Comparative Example 2

An ingot of an aluminum alloy A cast in Example 1 was subjected to scalping of rolling surface, homogenization, and hot rolling under conditions shown in Table 4. The hot-rolled product was cold-rolled to a thickness shown in Table 4 without being subjected to process annealing. Table 5 shows the surface roughness of a roll and the viscosity of a rolling oil used for cold rolling. In Tables 4 and 5, a value outside the condition according to the present invention is underlined.

The amount of aluminum powder on the surface of the sheet after cold rolling, the number of precipitates with a diameter of 0.1 to 1.0 μm, the number of oil pits with a diameter of 30 μm or more formed in the surface of the sheet, and the crystal grain size of the resulting aluminum alloy sheet (specimen) were measured according to the above-described methods. The results are shown in Table 5. Evaluation of burning resistance, observation of the presence or absence of scratches due to rubbing which occurred on a coil wound after cold rolling, an irregular pattern, and streaks, and evaluation of etching properties were conducted according to the above-described methods. The results are shown in Table 6.

TABLE 4 Cold Homogenization treatment Hot rolling rolling Amount of Temperature Temperature Start Finish Sheet Sheet scalping increase rate Temperature Time decrease rate temperature temperature thickness thickness Specimen (mm/side) (° C./hr) (° C.) (hr) (° C./hr) (° C.) (° C.) (mm) (mm) Remarks 15 5 37 538 3 35 470 355 3 0.3 Example 16 10  40 460 5 35 384 336 5 0.3 Example 17   1.5 31 502 2 35 450 340 2 0.3 Comparative Example 18 6 10 580 4 35 491 370 4 0.3 Comparative Example 19 7 70 580 4 35 479 366 4 0.3 Comparative Example 20 7 34 410 3 35 400 329 3 0.3 Comparative Example 21 8 35 610 3 35 411 333 3 0.3 Comparative Example 22 4 37 538   0.5 35 473 350 3 0.3 Comparative Example 23 9 29 595 5 35 331 272 3 0.3 Comparative Example 24 9 27 598 5 35 515 420 3 0.3 Comparative Example 25 12  40 460 5 35 388 341   6.5 0.3 Comparative Example 26 5 35 545 3 35 470 355 3 0.3 Comparative Example 27 5 35 545 3 35 465 339 3 0.3 Comparative Example 28 5 35 545 3 35 468 342 3 0.3 Comparative Example 29 5 35 545 3 35 475 332 3 0.3 Comparative Example

TABLE 5 Number of oil Viscosity Amount of pits with Ra ρ of Relationship I Relationship II aluminum diameter of 30 μm Crystal Crystal of roll rolling oil between between powder Precipitate or more length GL width GT Ratio Specimen (μm) (cSt) Mg and ρ Mg and ρ (mg/m²) (/mm²) (/mm²) (μm) (μm) GL/GT 15 0.3 3 Good Good 2.42 67920 41 641 62 10.3 16 0.3 3 Good Good 1.95 97850 32 1621 90 18.0 17 0.3 3 Good Good 2.64 76400 47 368 51  7.2 18 0.3 3 Good Good 1.50 113700  32 1052 79 13.3 19 0.3 3 Good Good 1.78  8080 29 979 76 12.9 20 0.3 3 Good Good 2.88  9160 33 910 89 10.2 21 0.3 3 Good Good 2.35  4520 22 822 76 10.8 22 0.3 3 Good Good 1.64  5910 18 626 66  9.5 23 0.3 3 Good Good 2.74 54220 35 Not Not — recrystallized recrystallized 24 0.3 3 Good Good 2.56 60030 42 1190 125   9.5 25 0.3 3 Good Good 1.39 81250 31 4115 189  21.8 26  0.05 3 Good Good 0.07 63600 71 400 54  7.4 27 0.6 3 Good Good 10.05  69450  6 512 55  9.3 28 0.3   0.5 Bad Good 3.80 60900  6 620 63  9.8 29 0.3 7 Bad Bad 0.04  7170 96 385 50  7.7 Note: Relationship I between Mg and ρ: −2 × Mg % + 2 ≦ ρ ≦ −2 × Mg % + 8 (satisfied: Good, not satisfied: Bad) Relationship II between Mg and ρ: ρ ≦ 2 × Mg % + 4 (satisfied: Good, not satisfied: Bad)

TABLE 6 Burning resistance Specimen (MPa) Scratch Unetched area Pit uniformity Irregular pattern Streaks 15 143 Excellent Excellent Excellent Good Good 16 126 Good Good Good Good Good 17 140 Excellent Good Good Good Bad 18 94 Good Good Bad Good Good 19 156 Good Bad Bad Good Good 20 160 Excellent Bad Bad Good Good 21 159 Excellent Bad Bad Good Good 22 166 Good Bad Bad Good Good 23 89 Excellent Good Good Bad Bad 24 165 Excellent Good Good Bad Good 25 125 Good Good Good Bad Good 26 130 Bad Good Bad Good Good 27 125 Excellent Bad Bad Bad Good 28 146 Excellent Bad Bad Bad Good 29 135 Bad Good Bad Good Good

As shown in Table 6, specimens No. 15 and No. 16 according to the present invention did not show scratches due to rubbing, exhibited excellent burning resistance, did not produce an irregular pattern and streaks, exhibited excellent etching properties after the electrolytic treatment, and had uniform etch pits over the entire surface. Specimen No. 17 produced streaks due to a small amount of scalping. In specimen No. 18, since the temperature increase rate of the ingot during the homogenization treatment was low, the diameter of the precipitates exceeded 1 μm and the number of precipitates decreased. Formation of pits was non-uniform due to the presence of an unetched area. Moreover, since the amount of precipitation increased to a large extent, the quantity of Fe in solid solution became insufficient, whereby burning resistance decreased. In specimen No. 19, since the temperature increase rate of the ingot during the homogenization treatment was high, precipitation did not proceed sufficiently so that pit starting points were insufficiently formed. An unetched area was formed during the electrolytic treatment, and uniformity of pits was impaired. In specimen No. 20, since the homogenization treatment temperature was low, precipitation of Fe and Si which serve as pit starting points was insufficient so that an unetched area was formed during the electrolytic treatment. As a result, the pit pattern became non-uniform. In specimen No. 21, since the homogenization treatment temperature was high, The quantity of Fe in solid solution increased. As a result, the number of minute precipitates which serve as pit starting points decreased. An unetched area was formed, and the pit pattern became non-uniform. In specimen No. 22, since the homogenization treatment time was short, precipitation of Fe and Si became insufficient, whereby the pit pattern became non-uniform due to formation of an unetched area. In specimen No. 22, since the hot rolling start temperature was low, the hot rolling finish temperature decreased. As a result, recrystallization occurred only partially, whereby streaks occurred. Moreover, since the amount of strain accumulated after final cold rolling increased, the recrystallizing temperature decreased, whereby burning resistance decreased. In specimen No. 24, since the hot rolling start temperature was high, the hot rolling finish temperature increased. Although recrystallization occurred over the entire surface, coarse crystal grains were formed, whereby irregular surface quality and streaks occurred. In specimen No. 25, since the thickness of the sheet when finishing hot rolling was large, the rolling rate during hot rolling became insufficient so that the amount of strain introduced decreased, whereby recrystallized grains became coarse. As a result, the surface quality became irregular. In specimen No. 26, since the arithmetic average roughness of the roll surface was small, the amount of rolling oil introduced between the roll and the rolled sheet increased to a large extent, whereby the number of large oil pits increased. As a result, etch pits formed during the electrolytic surface-roughening treatment became non-uniform. Moreover, since the amount of powder decreased, scratches due to rubbing were observed. In specimen No. 27, since the arithmetic average roughness of the roll surface was large, the amount of rolling oil introduced between the roll and the rolled sheet decreased, whereby a lubrication failure occurred. As a result, the amount of powder increased, whereby formation of pits became non-uniform. An inferior appearance due to an unetched area or an irregular pattern occurred after electrolytic graining. In specimen No. 27, since the viscosity of the rolling oil was low, the amount of rolling oil introduced between the roll and the rolled sheet decreased, whereby a lubrication failure occurred. As a result, the amount of aluminum powder increased, whereby formation of pits became non-uniform. An inferior appearance due to an unetched area or an irregular pattern occurred after electrolytic graining. In specimen No. 29, since the viscosity of the rolling oil was high, the amount of rolling oil introduced between the roll and the rolled sheet increased to a large extent, whereby the number of large oil pits increased. As a result, etch pits formed during the electrolytic surface-roughening treatment became non-uniform. Moreover, since the amount of powder decreased, coil scratches due to rubbing were observed.

Example 3 and Comparative Example 3

Each rolling side of an ingot of an aluminum alloy (Table 1) cast in Example 1 was faced by 5 mm to reduce the thickness of the ingot to 500 mm. The ingot was heated to 530° C. at a temperature increase rate of 35° C./hr. The ingot was then subjected to homogenization at 530° C. for 3.5 hours.

The ingot was heated to 469° C. (hot rolling start temperature) and was then hot-rolled to a thickness of 3 mm. Hot rolling was finished at 353° C. The hot-rolled product was cold-rolled to a thickness of 0.3 mm without being subjected to process annealing. The arithmetic average roughness Ra of a roll used for cold rolling was 0.3 μm, and the viscosity of a rolling oil was 3 cSt.

The amount of aluminum powder on the surface of the sheet after cold rolling, the number of precipitates with a diameter of 0.1 to 1.0 μm, the number of oil pits with a diameter of 30 μm or more formed in the surface of the sheet, and the crystal grain size of the resulting aluminum alloy sheet (specimen) were measured according to the above-described methods. The quantity of Fe in solid solution was measured according to the following method. The results are shown in Table 7. Evaluation of burning resistance, observation of the presence or absence of scratches due to rubbing which occurred on a coil wound after cold rolling, an irregular pattern, and streaks, and evaluation of etching properties were conducted according to the above-described methods. The results are shown in Table 8. In Table 7, a value outside the condition according to the present invention is underlined.

Measurement of the quantity of Fe in solid solution: The aluminum alloy sheet was dissolved in hot phenol, and the Fe content of the filtrate was measured. The details are described in “Measurement of amount of dissolution by wet chemical analysis” in Light Metal vol. 50 (2000), pages 518 to 526.

TABLE 7 Number of oil Viscosity Amount of pits with ρ of Relationship I Relationship II aluminum diameter of 30 μm Crystal Crystal Ra of roll rolling oil between between powder Precipitate or more length GL width GT Ratio Specimen (μm) (cSt) Mg and ρ Mg and ρ (mg/m²) (/mm²) (/mm²) (μm) (μm) GL/GT 30 0.3 3 Good Good 2.35 70030 41 35 63 10.4 31 0.3 3 Good Good 2.78 31200 30 46 75 10.7 32 0.3 3 Good Good 1.92 73510 53 38 65 9.7 33 0.3 3 Good Good 0.10 66780 92 7 61 11.3 34 0.3 3 Good Good 2.71 73150 47 40 70 9.4 35 0.3 3 Bad Good 4.20 60060 30 88 67 10.6 36 0.3 3 Bad Good 0.02 62390 26 2 73 10.4 37 0.3 3 Good Good 0.30 60840 44 15 70 10.6 38 0.3 3 Good Good 3.24  7120 15 51 135  10.7 39 0.3 3 Good Good 1.00 167000  120  20 48 10.9 40 0.3 3 Good Good 2.51 65110 30 40 62 10.6 41 0.3 3 Good Good 1.59 59430 28 29 59 10.0 42 0.3 3 Good Good 0.66 81000 86 23 57 10.5 43 0.3 3 Good Good 2.30 62070 21 34 97 10.8 Note: Relationship I between Mg and ρ: −2 × Mg % + 2 ≦ ρ ≦ −2 × Mg % + 8 (satisfied: Good, not satisfied: Bad) Relationship II between Mg and ρ: ρ ≦ 2 × Mg % + 4 (satisfied: Good, not satisfied: Bad)

TABLE 8 Burning resistance Specimen (MPa) Scratch Unetched area Pit uniformity Irregular pattern Streaks 30 140 Good Excellent Excellent Good Good 31 132 Good Excellent Excellent Good Good 32 166 Good Excellent Excellent Good Bad 33 210 Good Good Good Good Good 34 138 Good Good Good Good Good 35 88 Good Bad Bad Bad Good 36 243 Bad Good Bad Good Good 37 205 Good Good Bad Good Good 38 95 Good Bad Bad Bad Good 39 200 Good Good Bad Good Good 40 142 Good Bad Bad Good Good 41 189 Good Good Bad Good Good 42 209 Good Good Bad Good Good 43 171 Good Good Bad Good Good

As shown in Table 8, specimens No. 30 to No. 34 according to the present invention did not show scratches due to rubbing, exhibited excellent burning resistance, did not produce an irregular pattern and streaks, exhibited excellent etching properties after the electrolytic treatment, and had uniform etch pits over the entire surface. On the other hand, specimen No. 35 exhibited inferior burning resistance due to low Mg content. Moreover, the amount of aluminum powder increased, and formation of pits became non-uniform. An inferior appearance due to an unetched area and an irregular pattern occurred after electrolytic graining. Specimen No. 36 exhibited inferior pit uniformity due to high Mg content. Moreover, the amount of aluminum powder decreased, and coil scratches due to rubbing occurred. Specimen No. 37 was non-uniformly surface-roughened due to high Zn content. Specimen No. 38 had a small number of precipitates due to low Fe content and low Si content. The distribution of Al—Fe intermetallic compounds and Al—Fe—Si intermetallic compounds became non-uniform, whereby formation of pits became non-uniform due to formation of an unetched area. Moreover, since the quantity of Fe in solid solution was small, burning resistance was insufficient. Specimen No. 39 produced a large number of precipitates due to high Fe content and high Si content to produce coarse compounds. Therefore, uniformity of the surface-roughened structure decreased. Moreover, since the quantity of Fe in solid solution was large, the pit pattern became non-uniform. In specimen No. 40, an unetched area occurred during the electrolytic treatment due to high Cu content so that pits became large and non-uniform. Specimen No. 41 produced coarse Al—Ti compounds due to high Ti content, whereby the surface-roughened structure became non-uniform. Specimen No. 42 produced coarse Al—Fe—Mn compounds or Al—Fe—Mn—Si compounds due to high Mn content, whereby surface roughening during the electrolytic treatment became non-uniform. In specimen No. 43, the shape of pits was deformed and became non-uniform since the total amount of Pb, In, Sn, and Ga exceeded 0.05%.

Example 4 and Comparative Example 4

An ingot of an aluminum alloy B cast in Example 1 was subjected to scalping of rolling surface, homogenization, and hot rolling under conditions shown in Table 9. The hot-rolled product was cold-rolled to a thickness shown in Table 9 without being subjected to process annealing. The ingot was cooled to room temperature after the homogenization treatment, and was then heated to the hot rolling start temperature. Table 10 shows the surface roughness of a roll and the viscosity of a rolling oil used for cold rolling. In Tables 9 and 10, a value outside the condition according to the present invention is underlined.

The amount of aluminum powder on the surface of the sheet after cold rolling, the number of precipitates with a diameter of 0.1 to 1.0 μm, the quantity of Fe in solid solution, the number of oil pits with a diameter of 30 μm or more formed in the surface of the sheet, and the crystal grain size of the resulting aluminum alloy sheet (specimen) were measured according to the above-described methods. The results are shown in Table 10. Evaluation of burning resistance, observation of the presence or absence of scratches due to rubbing which occurred on a coil wound after cold rolling, an irregular pattern, and streaks, and evaluation of etching properties were conducted according to the above-described methods. The results are shown in Table 11.

TABLE 9 Homogenization treatment Hot rolling Amount of Temperature Temperature Start Finish Cold rolling scalping increase rate Temperature decrease rate temperature temperature Sheet thickness Sheet thickness Specimen Alloy (mm/side) (° C./hr) (° C.) (° C./hr) (° C.) (° C.) (mm) (mm) Remarks 44 B 5 35 535 3 475 355 3 0.3 Example 45 B 5 44 455 10  475 355 3 0.3 Example 46 B 5 10 550 5 475 355 3 0.3 Comparative Example 47 B 5 80 580 2 475 355 3 0.3 Comparative Example 48 B 5 38 405 3 475 355 3 0.3 Comparative Example 49 B 5 30 615 3 475 355 3 0.3 Comparative Example 50 B 5 33 553   0.5 475 355 3 0.3 Comparative Example

TABLE 10 Number of Quantity oil pits with Viscosity Amount of of diameter Ra ρ of Relationship I Relationship II aluminum Fe in solid of 30 μm Crystal Crystal of roll rolling oil between between powder Precipitate solution or more length GL width GT Ratio Specimen (μm) (cSt) Mg and ρ Mg and ρ (mg/m²) per mm² (ppm) (/mm²) (μm) (μm) GL/GT 44 0.3 3 Good Good 2.38 55230  26 50 735 73 10.1 45 0.3 3 Good Good 1.80 69410  21 40 843 90 9.4 46 0.3 3 Good Good 1.71 9830 17 35 1120 98 11.4 47 0.3 3 Good Good 1.67 3120 172  36 964 92 10.5 48 0.3 3 Good Good 2.93 7040 116  38 900 89 10.1 49 0.3 3 Good Good 2.40 3950 129  24 850 87 9.8 50 0.3 3 Good Good 1.59 3760 30 21 671 63 10.7 Note: Relationship I between Mg and ρ: −2 × Mg % + 2 ≦ ρ ≦ −2 × Mg % + 8 (satisfied: Good, not satisfied: Bad) Relationship II between Mg and ρ: ρ ≦ 2 × Mg % + 4 (satisfied: Good, not satisfied: Bad)

TABLE 11 Burning resistance Specimen (MPa) Scratch Unetched area Pit uniformity Irregular pattern Streaks 44 130 Excellent Good Good Good Good 45 122 Good Good Good Good Good 46 72 Good Bad Bad Good Good 47 123 Good Bad Bad Good Good 48 136 Excellent Bad Bad Good Good 49 140 Excellent Bad Bad Good Good 50 144 Good Bad Bad Good Good

As shown in Table 11, specimens No. 44 and No. 45 according to the present invention did not show scratches due to rubbing, exhibited excellent burning resistance, did not produce an irregular pattern and streaks, exhibited excellent etching properties after the electrolytic treatment, and had uniform etch pits over the entire surface. In specimen No. 46, since the temperature increase rate of the ingot during the homogenization treatment was low, the diameter of the precipitates exceeded 1 μm and the number of precipitates decreased. Therefore, an unetched area was formed so that uniformity of pits was poor. Moreover, since the amount of precipitation increased to a large extent, the quantity of Fe in solid solution became insufficient, whereby burning resistance decreased. In specimen No. 47, since the temperature increase rate of the ingot during the homogenization treatment was high, precipitation became insufficient, whereby the pit pattern became non-uniform due to formation of an unetched area during the electrolytic treatment. In specimen No. 48, since the homogenization treatment temperature was low, precipitation of Fe and Si (i.e., a reduction in the quantity of Fe and Si in solid solution) became insufficient, whereby the pit pattern became non-uniform due to formation of an unetched area during the electrolytic treatment. In specimen No. 49, since the homogenization treatment temperature was high, the quantity of Fe in solid solution increased. As a result, the number of minute precipitates which serve as pit starting points decreased. An unetched area was formed, and the pit pattern became non-uniform. In specimen No. 50, since the homogenization treatment time was short, the dissolution state of Fe and Si in the longitudinal direction and the width direction became non-uniform, whereby the pit pattern became non-uniform.

Example 5 and Comparative Example 5

Each rolling side of an ingot of an aluminum alloy (Table 1) cast in Example 1 was faced by 5 mm to reduce the thickness of the ingot to 500 mm. The ingot was heated to 530° C. at a temperature increase rate of 35° C./hr, and was then subjected to homogenization at 530° C. for 3.5 hours.

The temperature of the ingot was decreased to 490° C. (hot rolling start temperature) at a temperature decrease rate of 35° C./hr. The ingot was then hot-rolled to a thickness of 3 mm. Hot rolling was finished at 346° C. The hot-rolled product was cold-rolled to a thickness of 0.3 mm without being subjected to process annealing. The arithmetic average roughness Ra of a roll used for cold rolling was 0.3 μm, and the viscosity of a rolling oil was 3 cSt.

The amount of aluminum powder on the surface of the sheet after cold rolling, the number of precipitates with a diameter of 0.1 to 1.0 μm, the quantity of Fe in solid solution, the number of oil pits with a diameter of 30 μm or more formed in the surface of the sheet, and the crystal grain size of the resulting aluminum alloy sheet (specimen) were measured according to the above-described methods. The content (%) of Fe (Fe compound) which formed an intermetallic compound with respect to the total Fe content, the content (%) of Si (Si compound) which formed an intermetallic compound with respect to the total Si content, and the ratio (B %/A %) of the content (B %) of Fe which formed an Al—Fe—Si intermetallic compound to the content (A %) of Fe which formed an Al—Fe intermetallic compound were determined according to the following method. The results are shown in Table 12. Evaluation of burning resistance, observation of the presence or absence of scratches due to rubbing which occurred on a coil wound after cold rolling, an irregular pattern, and streaks, and evaluation of etching properties were conducted according to the above-described methods. The results are shown in Table 13. In FIG. 12, a value outside the condition according to the present invention is underlined.

Measurement of Fe content and Si content relating to intermetallic compound: The Fe content and the Si content of the total intermetallic compounds were determined using a phenol residue analysis method shown in FIG. 2. The ratio (Fe content (wt %) of Al—Fe—Si intermetallic compounds)/(Fe content (wt %) of Al—Fe intermetallic compounds) of the total intermetallic compounds was determined.

TABLE 12 Viscosity Quantity ρ Amount of of Fe in Ra of rolling Relationship Relationship aluminum solid Fe of roll oil I between II between powder Precipitate solution compound Specimen (μm) (cSt) Mg and ρ Mg and ρ (mg/m²) (/mm²) (ppm) (%) 51 0.3 3 Good Good 2.43 67430 53 98.3 52 0.3 3 Good Good 2.91 30060 29 98.2 53 0.3 3 Good Good 1.88 74600 61 97.8 54 0.3 3 Good Good 0.20 62890 80 98.0 55 0.3 3 Good Good 2.58 72650 40 98.8 56 0.3 3 Bad Good 4.11 61120 33 98.9 57 0.3 3 Bad Good 0.03 64210 27 98.9 58 0.3 3 Good Good 0.26 59330 39 98.7 59 0.3 3 Good Good 3.19  5300 13 97.8 60 0.3 3 Good Good 0.99 139720  162  98.0 61 0.3 3 Good Good 2.47 67940 31 99.0 62 0.3 3 Good Good 1.81 58040 36 98.6 63 0.3 3 Good Good 0.55 82180 92 97.5 64 0.3 3 Good Good 2.51 61040 20 98.3 Number of oil pits with Si diameter of 30 μm Crystal Crystal compound or more length GL width GT Ratio Specimen (%) B %/A % (/mm²) (μm) (μm) GL/GT 51 20.0 0.23 38 661 64 10.3 52 23.3 0.27 47 820 77 10.6 53 17.8 0.38 33 634 68 9.3 54 35.7 0.43 6 679 63 10.8 55 34.3 0.53 42 632 58 10.9 56 18.3 0.21 71 733 66 11.1 57 20.0 0.24 3 756 79 9.6 58 31.4 0.51 13 727 78 9.3 59 60.0 0.93 49 1220 131  9.3 60  7.1 0.10 23 529 47 11.3 61 32.9 0.58 45 603 60 10.1 62 12.3 0.44 30 601 60 10.0 63 22.0 0.17 19 588 55 10.7 64 10.0 0.78 33 1075 99 10.9 Note: Relationship I between Mg and ρ: −2 × Mg % + 2 ≦ ρ ≦ −2 × Mg % + 8 (satisfied: Good, not satisfied: Bad) Relationship II between Mg and ρ: ρ ≦ 2 × Mg % + 4 (satisfied: Good, not satisfied: Bad)

TABLE 13 Burning resistance Specimen (MPa) Scratch Unetched area Pit uniformity Irregular pattern Streaks 51 155 Good Excellent Excellent Good Good 52 140 Good Excellent Excellent Good Good 53 162 Good Excellent Excellent Good Good 54 220 Good Good Good Good Good 55 134 Good Good Good Good Good 56 90 Good Bad Bad Bad Good 57 233 Bad Good Bad Good Good 58 198 Good Good Bad Good Good 59 93 Good Bad Bad Bad Good 60 204 Good Good Bad Good Good 61 147 Good Bad Bad Good Good 62 186 Good Good Bad Good Good 63 199 Good Good Bad Good Good 64 175 Good Good Bad Good Good

As shown in Table 13, specimens No. 51 to No. 55 according to the present invention did not show scratches due to rubbing, exhibited excellent burning resistance, did not produce an irregular pattern and streaks, exhibited excellent etching properties after the electrolytic treatment, and had uniform etch pits over the entire surface. On the other hand, specimen No. 56 exhibited inferior burning resistance due to low Mg content. Moreover, the amount of aluminum powder increased, and formation of pits became non-uniform. An inferior appearance due to an unetched area and an irregular pattern occurred after electrolytic graining. Specimen No. 57 exhibited inferior pit uniformity due to high Mg content. Moreover, the amount of aluminum powder decreased, and coil scratches due to rubbing occurred. Specimen No. 58 was non-uniformly surface-roughened due to high Zn content. Specimen No. 59 had a small number of precipitates due to low Fe content and low Si content. The distribution of Al—Fe intermetallic compounds and Al—Fe—Si intermetallic compounds became a non-uniform, whereby formation of pits became non-uniform due to formation of an unetched area. Moreover, since the quantity of Fe in solid solution was small, burning resistance was insufficient. Since the content of Fe which formed an intermetallic compound was more than 40% of the total Fe content, precipitation of Al—Fe—Si intermetallic compounds which serve as pit starting points to only a small extent proceeded so that large pits were formed due to a decrease in pit formation efficiency. As a result, the pit pattern became non-uniform. When the ratio (B %/A %) of the content (B %) of Fe which forms an Al—Fe—Si intermetallic compound to the content (A %) of Fe which forms an Al—Fe intermetallic compound is larger than 0.9, large pits tend to be formed due to a decrease in pit formation efficiency. Specimen No. 60 produced a large number of precipitates due to high Fe content and high Si content to produce coarse compounds. Therefore, uniformity of the surface-roughened structure decreased. Moreover, since the quantity of Fe in solid solution was large, the pit pattern became non-uniform. In specimen No. 61, an unetched area occurred during the electrolytic treatment due to high Cu content so that pits became large and non-uniform. Specimen No. 62 produced coarse Al—Ti compounds due to high Ti content, whereby the surface-roughened structure became non-uniform. Specimen No. 63 produced coarse Al—Fe—Mn compounds or Al—Fe—Mn—Si compounds due to high Mn content, whereby surface roughening during the electrolytic treatment became non-uniform. In specimen No. 64, the shape of pits was deformed and became non-uniform since the total amount of Pb, In, Sn, and Ga exceeded 0.05%.

Example 6 and Comparative Example 6

An ingot of an aluminum alloy C cast in Example 1 was subjected to scalping of rolling surface, homogenization, and hot rolling under conditions shown in Table 14. The hot-rolled product was cold-rolled to a thickness shown in Table 14 without being subjected to process annealing. The ingot was cooled to room temperature after the homogenization treatment, and was then heated to the hot rolling start temperature. Table 15 shows the surface roughness of a roll and the viscosity of a rolling oil used for cold rolling. In Tables 14 and 15, a value outside the condition according to the present invention is underlined.

The amount of aluminum powder on the surface of the sheet after cold rolling, the number of precipitates with a diameter of 0.1 to 1.0 μm, the quantity of Fe in solid solution, the content (%) of Fe (Fe compound) which formed an intermetallic compound with respect to the total Fe content, the content (%) of Si (Si compound) which formed an intermetallic compound with respect to the total Si content, and the ratio (B %/A %) of the content (B %) of Fe which formed an Al—Fe—Si intermetallic compound to the content (A %) of Fe which formed an Al—Fe intermetallic compound, the number of oil pits with a diameter of 30 μm or more formed in the surface of the sheet, the crystal grain size, the content of Fe which formed an intermetallic compound, the content of Si which formed an intermetallic compound, and the ratio of the content of Fe which formed an Al—Fe—Si intermetallic compound to the content of Fe which formed an Al—Fe intermetallic compound of the resulting aluminum alloy sheet (specimen) were measured according to the above-described methods. The results are shown in Table 15. Evaluation of burning resistance, observation of the presence or absence of scratches due to rubbing which occurred on a coil wound after cold rolling, an irregular pattern, and streaks, and evaluation of etching properties were conducted according to the above-described methods. The results are shown in Table 18.

TABLE 14 Homogenization treatment Hot rolling Cold rolling Amount of Temperature Temperature Start Finish Sheet Sheet scalping increase rate Temperature Time decrease rate temperature temperature thickness thickness Specimen Alloy (mm/side) (° C./hr) (° C.) (hr) (° C./hr) (° C.) (° C.) (mm) (mm) Remarks 65 C 5 35 535 3 35 465 343 3 0.3 Example 66 C 5 35 455 10  44 465 343 3 0.3 Example 67 C 5 35 405 5 30 465 343 3 0.3 Comparative Example 68 C 5 35 615 2 33 465 343 3 0.3 Comparative Example 69 C 5 35 550   0.5 38 465 343 3 0.3 Comparative Example 70 C 5 35 580 3 10 465 343 3 0.3 Comparative Example 71 C 5 35 553 3 80 465 343 3 0.3 Comparative Example

TABLE 15 Quantity Viscosity ρ Amount of of Fe in of rolling Relationship Relationship aluminum solid Ra of roll oil I between II between powder Precipitate solution Specimen (μm) (cSt) Mg and ρ Mg and ρ (mg/m²) (/mm²) (ppm) 65 0.3 3 Good Good 1.98 73240  24 66 0.3 3 Good Good 1.41 88780  31 67 0.3 3 Good Good 1.29 7330 120  68 0.3 3 Good Good 1.26 3420 168  69 0.3 3 Good Good 2.55 4040 55 70 0.3 3 Bad Good 2.00 9650 19 71 0.3 3 Bad Good 0.98 8870 80 Number of oil pits with Fe Si diameter of 30 μm Crystal Crystal compound compound or more length GL width GT Ratio Specimen (%) (%) B %/A % (/mm²) (μm) (μm) GL/GT 65 99.1 13.3 0.26 30 514 53 9.7 66 98.9 21.1 0.48 25 875 90 9.7 67 95.7 33.3 1.12 19 1130 108  10.5 68 94.0 8.9 0.17 16 836 82 10.2 69 98.0 10.0 0.18 20 713 66 10.8 70 99.3 32.2 0.97 14 850 87 9.8 71 97.1 8.9 0.16 10 547 52 10.5 Note: Relationship I between Mg and ρ: −2 × Mg % + 2 ≦ ρ ≦ −2 × Mg % + 8 (satisfied: Good, not satisfied: Bad) Relationship II between Mg and ρ: ρ ≦ 2 × Mg % + 4 (satisfied: Good, not satisfied: Bad)

TABLE 16 Burning resistance Specimen (MPa) Scratch Unetched area Pit uniformity Irregular pattern Streaks 65 148 Excellent Good Good Good Good 66 123 Good Good Good Good Good 67 140 Good Bad Bad Good Good 68 145 Good Bad Bad Good Good 69 137 Excellent Good Bad Good Good 70 79 Excellent Good Bad Good Good 71 126 Good Bad Bad Good Bad

As shown in Table 16, specimens No. 65 and No. 66 according to the present invention did not show scratches due to rubbing, exhibited excellent burning resistance, did not produce an irregular pattern and streaks, exhibited excellent etching properties after the electrolytic treatment, and had uniform etch pits over the entire surface. In specimen No. 67, since the homogenization treatment temperature was low, precipitation of Fe and Si which serve as pit starting points was insufficient so that an unetched area was formed during the electrolytic treatment. As a result, the pit pattern became non-uniform. In specimen No. 68, since the homogenization treatment temperature was high, the quantity of Fe in solid solution increased. As a result, the number of minutes precipitates which serve as pit starting points decreased. An unetched area was formed, and the pit pattern became non-uniform. In specimen No. 69, since the homogenization treatment time was short, precipitation of Fe and Si became insufficient, whereby the pit pattern became non-uniform. In specimen No. 70, since the temperature decrease rate of the ingot to the hot rolling start temperature after the homogenization treatment was low, precipitation of Al—Fe—Si intermetallic compounds proceeded, whereby the diameter of the precipitates exceeded 1 μm and the number of precipitates decreased. Moreover, the quantity of Fe in solid solution decreased. As a result, burning resistance became insufficient, and pits became non-uniform. In specimen No. 71, since the temperature decrease rate of the ingot to the hot rolling start temperature after the homogenization treatment was high, the period of time for precipitation was insufficient. Moreover, since the temperature of the ingot became non-uniform, precipitation of Fe and Si also became non-uniform. As a result, recrystallization during the subsequent hot rolling became non-uniform, whereby streaks occurred. In addition, the pit pattern became non-uniform.

INDUSTRIAL APPLICABILITY

According to the present invention, an aluminum alloy sheet for a lithographic printing plate which allows pits to be more uniformly formed by an electrochemical surface-roughening treatment, exhibits more excellent adhesion to a photosensitive film and water retention properties, and shows excellent strength and thermal softening resistance which achieve improved image clarity and plate wear, and a method of producing the same are provided. 

1. An aluminum alloy sheet for a lithographic printing plate, the aluminum alloy sheet comprising 0.1 to 1.5% (mass %; hereinafter the same) of Mg, 0.5% or less (excluding 0%; hereinafter the same) of Zn, 0.1 to 0.6% of Fe, 0.03 to 0.15% of Si, 0.0001 to 0.1% of Cu, and 0.0001 to 0.1% of Ti, with the balance being aluminum and impurities, the amount of aluminum powder on the surface of the aluminum alloy sheet being 0.1 to 3.0 mg/mm².
 2. An aluminum alloy sheet for a lithographic printing plate, the aluminum alloy sheet comprising 0.1 to 1.5% of Mg, more than 0.05% and 0.5% or less of Zn, 0.1 to 0.6% of Fe, 0.03 to 0.15% of Si, 0.0001 to 0.10% of Cu, and 0.0001 to 0.05% of Ti, with the balance being aluminum and impurities, the Mg content and the Zn content of the aluminum alloy sheet satisfying a relationship “4×Zn %−1.4%≦Mg %≦4×Zn %+0.6%”, and the amount of aluminum powder on the surface of the aluminum alloy sheet being 0.1 to 3.0 mg/m².
 3. The aluminum alloy sheet according to claim 2, wherein precipitates with a diameter (circle equivalent diameter) of 0.1 to 1.0 μm are dispersed on the surface of the aluminum alloy sheet in a number of 10,000 to 100,000 per square millimeter (mm²).
 4. The aluminum alloy sheet according to claim 2, wherein the quantity of Fe in solid solution in the aluminum alloy sheet is 20 to 100 ppm.
 5. The aluminum alloy sheet according to claim 2, wherein some or all of the elements of the aluminum alloy sheet form intermetallic compounds, the content of Fe which forms an intermetallic compound is 50 to 99.8% of the total Fe content, the content of Si which forms an intermetallic compound is 5 to 40% of the total Si content, and the ratio (B %/A %) of the content (B %) of Fe which forms an Al—Fe—Si intermetallic compound to the content (A %) of Fe which forms an Al—Fe intermetallic compound is 0.9 or less.
 6. The aluminum alloy sheet according to claim 1, wherein the number of oil pits with a diameter (circle equivalent diameter) of 30 μm or more formed in the surface of the aluminum alloy sheet is 50 or less per square millimeter (mm²).
 7. The aluminum alloy sheet according to claim 1, wherein the aluminum alloy sheet further comprises more than 0.05% and 0.3% or less of Mn.
 8. The aluminum alloy sheet according to claim 1, wherein the average grain size of the aluminum alloy sheet in a direction perpendicular to a rolling direction with respect to the surface of the aluminum alloy sheet is 100 μm or less, and the average grain size in a direction parallel to the rolling direction with respect to the surface of the aluminum alloy sheet is 2 to 20 times the average grain size in the direction perpendicular to the rolling direction.
 9. The aluminum alloy sheet according to claim 1, wherein the aluminum alloy sheet further comprises one or more elements selected from Pb, In, Sn, and Ga in an amount of 0.005 to 0.05% in total.
 10. The aluminum alloy sheet according to claim 3, wherein the aluminum alloy sheet has a 0.2% proof stress of 120 MPa or more after being subjected to a heat treatment at 270° C. for seven minutes.
 11. A method of producing an aluminum alloy sheet for a lithographic printing plate, the method comprising casting an aluminum alloy having the composition according to claim 2 to obtain an ingot, scalping a rolling-side surface of the ingot by 3 to 15 mm, subjecting the ingot to a homogenization treatment which includes heating the ingot to 450 to 580° C. at a temperature increase rate of 20 to 60° C./hr and keeping the ingot at 450 to 580° C. for one hour or more, hot-rolling the resulting product to a thickness of 5 mm or less under conditions where the hot rolling start temperature is 400 to 520° C. and the hot rolling finish temperature is 320 to 400° C., and cold-rolling the hot-rolled product without subjecting the hot-rolled product to process annealing.
 12. A method of producing an aluminum alloy sheet for a lithographic printing plate, the method comprising casting an aluminum alloy having the composition according to claim 2 to obtain an ingot, scalping a rolling-side surface of the ingot by 3 to 15 mm, subjecting the ingot to a homogenization treatment which includes heating the ingot to 450 to 580° C. at a temperature increase rate of 20 to 60° C./hr and keeping the ingot at 450 to 580° C. for one hour or more, cooling the resulting product to room temperature, heating the cooled product to 350 to 500° C. and hot-rolling the product to a thickness of 5 mm or less under conditions where the hot rolling finish temperature is 300 to 380° C., and cold-rolling the hot-rolled product without subjecting the hot-rolled product to process annealing.
 13. A method of producing an aluminum alloy sheet for a lithographic printing plate, the method comprising casting an aluminum alloy having the composition according to claim 2 to obtain an ingot, scalping a rolling-side surface of the ingot by 3 to 15 mm, subjecting the ingot to a homogenization treatment which includes heating the ingot to 450 to 580° C. and keeping the ingot at 450 to 580° C. for three hours or more, cooling the resulting product to a hot rolling start temperature at a temperature decrease rate of 20 to 60° C./hr, hot-rolling the cooled product to a thickness of 5 mm or less under conditions where the hot rolling start temperature is 400 to 500° C. and the hot rolling finish temperature is 300 to 400° C., and cold-rolling the hot-rolled product without subjecting the hot-rolled product to process annealing.
 14. A method of producing the aluminum alloy sheet according to claim 1, the method comprising subjecting the aluminum alloy sheet to final cold rolling using a rolling oil with a viscosity of 1 to 6 cSt.
 15. A method of producing the aluminum alloy sheet according to claim 1, the method comprising subjecting the aluminum alloy sheet to final cold rolling using a rolling oil, the Mg content (Mg %) of the aluminum alloy sheet and the viscosity p of the rolling oil satisfying a relationship “−2×Mg %+2≦ρ≦−2×Mg %+8”.
 16. A method of producing the aluminum alloy sheet according to claim 6, the method comprising subjecting the aluminum alloy sheet to final cold rolling using a roll having a roll surface with an arithmetic average roughness Ra of 0.2 to 0.5 μm and a rolling oil with a viscosity of 1 to cSt.
 17. A method of producing the aluminum alloy sheet according to claim 6, the method comprising subjecting the aluminum alloy sheet to final cold rolling using a rolling oil, the Mg content (Mg %) of the aluminum alloy sheet and the viscosity p of the rolling oil satisfying a relationship “ρ≦2×Mg+4”. 